Manufacture of mineral wool



Sept. 217, 1938. A.l T. SHRUM 2,131,599

` MANUFAOTURE OF MINERAL WOOL Filed Aug. es.l 1934 2 sheets-sheet 1.

.SUPPLY HoFPR INVENTOR Hr-hur Thrum ATTORNEY Sept. 27, 1938. A. T. SHRUM 2,131,599

MNUFACTURE OF MINERAL WOOL Filed Aug. 6, 1954 2 Sheets-Sheet 2 ATTORNEY Patented Sept. 27, 1938 UNITED STATES MANUFACTURE OF MINERAL WOOL Arthur T. Shrum,

mesne assignments, Youngstown, Ohio Poland, Ohio, assignor, by

to William C. Coryell,

Application August s, 1934, serial No. 738,619

2 Claims.

This invention relates to mineral wool, and particularlly to method of and apparatus for its production.

Mineral wool is produced by directing a stream 5 of molten slag, silica rock, or earthen fines, into a violent jet of steam or air. The jet discharges into a so-called blow-room, and ordinarily the stream of slag or other suitable material is caused freely to fall athwart the jet. As the steam Yprogressively encounters the jet, the molten material is progressively dispersed in the form of fine, lelongated shreds or ilbres. These fibres fall to the floor of the blow-room, where they form an interlaced, matted and fibrous mass which, when l5 the fibres cool and solidify, comprises mineral wool, or as it is commonly known, rock wool. Thisl wool is widely used as a heat-insulating material. l

In mineral wool, as it has hitherto been produced, there is found not only the desired glasslike fibres, but many small solid globules which are known as shot or beads. The shot content of the Wool varies, often running as high as fty percent. by weight, and, manifestly, in proportion to the relative quantity in which the shot is present, the heat-insulating properties of the wool are impaired. This situation has proved a problem to the art, and, in seeking a solution of such problem, I have made several important discoveries. I have discovered that the temperature and the' analysis of the molten material, immediately prior to its introduction to the blasting jet, has a direct bearing on the quantity of shot in the wool; additionally, I have found that the 3'5 temperature and motion of the air in the blowroom affect the quantity of shot in the wool, as

well as being partly instrumental in determining the length and physical characteristics of the fibres thereof. My invention lies in method of 40 and apparatus for readily controlling these factors, whereby I produce a Wool having either no shot content or a uniform, minimum shot content,-a wool whose fibres are long and possessive of the desired high flexibility and resistance to rupture.

Turning to a consideration of how the molten material is prepared for blowing into wool, it will be perceived that my invention embraces still other features. In passing, it may be remarked that in some cases the molten slag of a blast furnace (or other metallurgical furnace) has been directly employed as the material from which to blow mineral wool. Ingeneral, howover, it maybe said that the use of direct slag has proved unsatisfactory, because of the unv (Ci. t9-77.5)

controllable variations in slag analysis. So far as I am aware, the best prior practice has been to melt down-say by means of a cupola-a charge of material or materials of predetermined characteristics. The material (or materials) and coke 5 are placed in alternate layers in the cupola, until the cupola is filled, an'd, in accordance with usual cupola operation, air for the combustion of the coke is forced inward through tuyres located at or above the cupola hearth. rIhus, the massed layers of the material are melted and drawn off and blown into wool.

Contrary to this practice of mass melting, so to speak, I prepare the material in'pulverized or eomminuted condition, and progressively and continuously disseminate it through a fusing atmosphere. In passing through such atmosphere the particles of material are melted or preheated, whence' they are caused to enter a molten pool of the material, lwhich pool feeds a continuous stream tothe wool-forming jet. The feeding of the comminuted material may be continued indenitely, and may be eiected automatically; from moment to moment the kind and quality of the material fed through the fusing or preheating atmosphere may be selected and varied, so that the analysis of the molten pool may be held to desired valuepand the temperature of the fusing atmosphere may be regulated and the rate of feeding of the particles may be correspondingly adjusted, whereby the temperature and volume of the molten supply pool are subject to ready control. Accordingly, it bcomes possible to manufacture mineral wool in a continuous process ,-a continuous process in which the critical factors alluded to above are subject to adjustment and control, readily and in a moment. I may add, my invention admits of the use ofcertain desirable materials and slag fines which in the prior cupola practice mentioned could not be properly melted.

An object of this invention is to provide an apparatus and a method for producing mineral wool continuously which will be substantially free of shot and in cases where any shot is desired it will also be possible to regulate the shot content and make it uniform throughout the production.

Another object of the invention is to provide a method and apparatusv for producing numeral wool substantially uniform in quality with regard 5o to its chemical analysis, out of a slag that may be non-uniform in analysis.

A further object of the invention is to control the length of fiber of the material which is accom plished by controlling the temperature of the mol- .55

ten material and controlling the temperature of the blow-room and motion of the air currents set up in the blow-room.

Still a further object of the invention is to produce a mineral wool which will be superior in quality with regard to length and flexibility of fiber.

These and further objects will be more defi- -nitely explained and apparent from the description hereinafter contained.

In the accompanying drawings Fig. I is a view in vertical section of apparatus embodying the invention;

Fig. II is a similar View, illustrating certain modifications;

Fig. III is a View in cross-section, taken on the plane III-III of Fig. II.

Advantageously, the apparatus for the practice of my invention comprises a furnace having a tall shaft 3 extending upward from a firing chamber 30. The furnace is constructed of refractory material, reinforced and braced with steel where needed. Opening into the ilring chamber 30 is a plurality of burners I connected to a gaseous fuel supply (not shown) Enveloping and spaced from the body of shaft 3 is a jacket I I, connected by a down-comer IIa toa manifold I2, and conduits I2a extend from the manifold and severally communicate with the openings in the furnace Wall into which the burners I0 project. In service, the air for combustion of the fuel is preheated in jacket II, and passes into manifold I2 by way of down-comer IIa, whence it is drawn through passages I2a and enters the firing chamber 30 with the jets of fuel.

Beneath the firing chamber 30 is a hearth 30a, from which a discharge passage I4 extends to a discharge mouth I6. 'I'he bottom portion I3 of the furnace, including the hearth 30a', is preferably separablefrom the stack portion, so that it may be independently removed for repair.

Combustion of the fuel progresses in chamber 30 and the hot waste gases flow upwardly through the shaft 3 and into a chimney 3|. Adjacent the top of the shaft a cone 4 is secured, and the hot and burning gases in chamber 30 and shaft 3 are effective to provide the fusing atmosphere in which to disseminate the material, as already described. A chute 5 projects through the wall of shaft 3 and its discharge end is directed toward the cone or bell 4; a hopper 'I is maintained in supply with the comminuted material by means of an endless conveyor or elevator 8; and a vibrating feeder 6 (diagrammatically indicated, but of wellknown structure) controls the progressive feeding of material from the hopper 'I to the chute 5. rlfhe chute 5 may preferably be in the form of a closed pipe forming the casing of a spiral screw conveyor which will continuously feed the material to the furnace so that it will fall upon the bell 4and is thereby disseminated and scattered for descent through the fusing atmosphere. This pipemay be sealed against the internal pressure in the furnace when necessary to feed the furnace under pressure.

'Ihe small particles descend and float downward through the shaft against the upward, counter currents of hot gases. The velocity and temperature of these gases may be varied by regulating the quantity and pressure of air and fuel introduced into the firing chamber 30; conveniently a powerfully driven fan 32 in down-comer IIa is eective to maintain the preheated air in manifold I2 at super-atmospheric pressure, while adjustable dampers 33 in passages I2ar afford a more minute control of the air entering the combustion chamber. Manifestly, valvesin the fuel supply lines may be adapted to control the pressure and quantity of fuel fed into chamber 30. Accordingly, by so varying theupward velocity of gases in the shaft 3, the downward movement of the particles falling from bell 4 may be accelerated or retarded; by varying the quantity of fuel fed into the chamber 30, the temperature of the fusing atmosphere may be regulated, whereby compensation is made for variations in the particle size of the material fed into the shaft, and for variations in the rate of feeding, so that upon reaching the bottom of the chamber 30, the particles may be completely fused and form a molten pool on the hearth 30a.

In the practice of my invention the accessibility of each particle (and of the whole surface area of each particle) to the hot gases renders it possible to fuse certain materials which otherwise could not be properly fused. Thusgreater varieties of material may be used, and the eld from which the raw material is obtained is appreciably widened. While many of the falling particles will actually melt during falling some of them may reach the bath in a solid condition due to the difference in size of the particles. Those that are melted will tend to 'superheat and then the molten bath will equalize the temperature of the particles so that all of them will eventually be melted.

It may be remarked that the height of the stack may be designed to meet particular conditions'in the field. That is to say, if certainmaterial is diiiicult to fuse, other things being equal a higher stack will be used; if the material is readily fusible, a lower stack may be used. In actual tests I have found that blast furnace slag of 60 mesh particle size was well fused in a stack 20 feet high, and it appeared that good results are obtainable with particle sizes of from 40 to 100 mesh and a heating zone temperature of about 2700 F.

The feeding of material into the shaft 3 is so determined that a pool of relatively large volume is maintained on the hearth 30a, in which the temperature of varying sized particles become equalized. The viscosity and temperature of the molten material in the pool are maintained as desired, by regulating the rate of combustion in chamber 30. A continuous stream of molten material flows through passage I4, and falls from mouth I6 into a jet of steam delivered by pipe Il. This steam may be super-heated, the excess temperature being obtained by super-heating the steam in the furnace stack or in any other suitable manner. As already mentioned, the jet of steam (or other suitable fluid) blows the material into tails of fibres glasslike.-In accordance with known practice, a small quantity of oil may be introduced to steam line I1, to produce a more fluffy, flexible product. II'he jet is directed through an opening 23 in the wall I9 of blow-room I8, and as already mentioned the fibres fall to the floor of the blow-room and form a blanket of mineral wool thereon. The blowroom is an elongate room, a room of such dimensions that it is impossible for the molten slag to make contact with its walls before the fibers have been fully formed. As usual, the floor of the blow-room comprises the upper reach of an endless conveyor 20 for removing the wool, and by regulating the speed of the conveyor, it is possible to vary the thickness of said blanket,

steam jet unless this passage is full of molten d material. I have found that this objectionable condition may be remedied by providing a burner i5, to direct burning fuel into the passage Il adjacent its mouth I6, so that a slight pressure willbe formed at the mouth. Y

During the continuous wool-blowing operation, the hot steam jet aspirates cold air from the outer atmosphere inward, through the opening 23. 'I'he foregoing specification has mentioned how the temperature and air currents in the blow room have a very definite effect upon the physical characteristics of the fibres and upon the quantity of shot produced in the wool. In accordance with the invention. I stabilize and regulate atmospheric conditions within the blowroom. The quantity 4oi' heat entering the blowroom is supplied by the steam jet and the molten slag, and in my continuous process this heat supply, together with the chilling effect of the cold air entering opening 23, is of relatively constant value. Advantageously, I provide one or more vents 22 in the walls of the blow-room, say in the top Wall 2|; the vent area is adapted to be varied by gates 24 subject to the controlv of a line 25, whereby the escape of air, vapors, and dust from the blow-room may be established and maintained at constant rate. Thus in regulating the escape of the air and vapors from` the blow-room, the quantity of cold air entering opening 23 is regulated, and in consequence the atmospheric conditions within the blow-room are subject to the hand of the operator. Indeed, well-known thermostatic instmmentalities may be organized toshift the wire 25 automatically, or in other convenient manner may be adapted automatically to regulate the blow-room atmosphere.

In proceeding in accordance with this invention, I am able to produce a wool of superior character,-a wool whose fibres are long and flexible, and a wool having a shot content below l0 percent by weight.

It has always been realized that many advantages and economies might be effected, if molten slag direct from a blast furnace were used as the material of which to produce the wool, but as above remarked it has hitherto been impractical to use "direct slag, because of the variations in the analysis thereof. In providing for a continuous or progressive melting or suitable materal, as above described. it is possible from moment to moment to alter the material being fused, whereby it becomes feasible to use direct" slag, as will 'be understood upon referring to the modification illustrated in Figures i II and III.

The modified apparatus embodies the shaft l and feeding mechanism (4 to B) described in Figure I. The hearth 30h of the modified furnace is relatively large and is adapted to hold a large store 28 of slag, delivered from a sci-called vthimble 21 and entering the furnace through an inlet 26. The thimble is the usual type of railway vehicle used to transport molten slag from a blast furnace to a dump or other place of disposal.

Burners' I0 (Fig. 1I) are inserted above the hearth IIb, and serve to create the fusing atmosphere in the stack 3. It will not always be necessary under all conditions to use the burners Iii as electrodes will furnish heat to the bath material and convection will cause warm air currents to move up the furnace stack. When these air currents are suiliciently hot it will then not be necessary to use the burners I0 in this type of furnace.

The material fed into the stack 3 is of such chemical composition as to bring the pool 28 to desired analysis, and thus the blast furnace slag is rectified for conversion to mineral wool. I contemplate that electric current may also be employed to keep'the pool 2B at proper temperature, and to this end I show in exemplary way a plurality of electrodes 29 projecting into the pool. The position of the electrodes in the pool may be adjusted by a gear-and-ratchet mechanism |30 and slagheating electric currents are caused to iiow in the pool from one electrode to another. y

The molten material passes from the hearth 30h by way of passage I4, and is blown into wool in the manner already described.

I have used the word continuous" in this specification and in the claims to mean that material can be fed into the furnace melted and run out continuously to distinguish it from the process of charging a furnace similar to a cupola 'with a certain definite chargeand melting it down to produce a given` quantity of molten mateial. In my invention it is possible to continuoui ly feed and melt and run the material out without depending upon a single charge and a single melt ing period.

While I have shown and described the preferred embodiment of my invention, it is to be understood that various changes in the apparatus and method may be made without departing from 'the' spirit of the invention or the scope of my broader claims.

Having thus clearly described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of making mineral wool which comprises, continuously feeding particles of a mass of comminuted ne mineral material of a size between 40 and 100 mesh in a region of heated and upwardly owing gases whereby the material is pre-heated, progressing the particles in a freely falling manner and at a determined rate through the' heating region for a sufficient length of time to melt the heated particles, coilecting the molten material in a pool, discharging the molten material from the pool, and thereafter blowing the discharged molten material to break it down into a fibrous condition.

2. The method of making mineral wool which comprises, forming a pool of molten mineral material, adding molten mineral material to said pool in bulk, feeding particles of a mass of cornminuted fine mineral lmaterial of selected composition and of a size between 46 and 100 mesh in a region of heated and upwardly flowing gases whereby the particles are pre-heated, progressing the particles in a freely falling manner and a determined rate through the heating region for a sufficient length of time to melt the heated particles, collecting the melted particles in the pool, discharging the molten material from the pool, and thereafter blowing the discharged molten material to break it down into a fibrous condition.

ARTHUR T. SHRUM. 

